This invention relates to code identification apparatus of the type in which an instrument such as a key or card having a code recorded on it is submitted to a reader which reads the recorded code. Apparatus of this type may be used in locking systems and various accounting and credit control facilities. In the case of a locking system the reader would control the condition of a lock and the coded instrument would normally be in the form of a key which is inserted into the reader. In the case of credit control systems the instrument would usually be in the form of a coded card.
The invention has particular, but not exclusive application to apparatus in which the instrument is magnetically coded, for example by the inclusion of small magnets at selected locations within a magnetic body of the instrument. Australian Pat. No. 65612/74 and granted U.S. Pat. No. 3,953,712 disclose an apparatus of this type in which a magnetically coded instrument is inserted into a guideway of a reader which includes a number of sensing coils disposed adjacent the guideway such that electromotive forces are generated in the sensing coils by movement of the magnetised portions of the instrument across them as the instrument approaches the end of its forward travel along the guideway. The electromotive forces generated in the sensing coils are amplified and influence the condition of an output circuit so as to cause generation of an output signal. Co-pending Australian patent application no. PC 7034/76 corresponding to U.S. patent application Ser. No. 769,532, filed Feb. 17, 1977, also discloses an apparatus in which a magnetically coded instrument is inserted into a guideway of a reader which reads its code. In that case the magnetised portions of the instrument are detected by a series of Hall Effect devices disposed within the reader adjacent the guideway.
In both of the above described arrangements the number of sensing elements incorporated in the reader is equal to the number of coding locations on the instrument and the code is read virtually instantaneously when the instrument approaches or reaches the end of its forward travel. The present invention provides an alternative arrangement which permits the number of sensing elements to be reduced.